The present invention relates to a device for driving an elongate cylindrical rotary body which is required to make contact with another similar rotary body with an even pressure distribution along its length, e. g. a register roller of a machine for electrophotography, a developing roller of a contact type developing system, or a doctor roller of a developing apparatus.
Generally, when a cylindrical axially elongate rotary body is to be rotated in even contact with another rotary body which is rotatable in a fixed position and may also be cylindrical and axially elongate, it is undesirable to fix the axes of the two rotary bodies in position. This is because, should the axes be fixed, the outer peripheries of the two rotary bodies would fail to make contact with an even pressure distribution due to the scattering in the degree of circularity and that of linearity. Here, the words "circularity" and "linearity" of a rotary body should be understood to imply, respectively, the equality of radii as measured from the axis and the straightness of the outer periphery as measured in the lengthwise direction. It is, therefore, a common practice to urge the rotary body, which is to be rotated in contact with the other which is fixed in position, in a predetermined direction toward the latter by, for example, a spring, thereby forcing them into contact with each other. Such a scheme, however, gives no consideration to the magnitude, direction and others of a force which is applied from a driving section to the rotary body whose axis is movable. Specifically, assuming that the movable rotary body is driven in a rotary motion at only one of its opposite ends, the contact pressure differs from that driven end to the other end resulting that an even contact pressure distribution is unattainable in the lengthwise or axial direction of the rotary body. This is true with, for example, a register roller of a sheet feed mechanism, a doctor roller of a developing device, and others, not to speak of a photoconductive element and a developing roller.